Atmel datasheet for the AT89C4051, a compact 20-pin 8051-compatible microcontroller with 4 KB of flash and an onboard analog comparator. The PDF covers the pinout, reduced port set, memory map, power modes and the parallel programming procedure. Such controllers turn up in timers, small appliances, chargers and kits, and the sheet helps when checking the crystal, reset and comparator pins. Programming needs a device programmer supporting the part rather than ISP; read and back up the old code if lock bits permit.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @datasheet. Enginerys does not host this file.
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